Method
The best way to barbecue this cut of lamb is long and slow. To achieve that tender fall off the bone result, we are going to barbecue using the indirect method.

Make 3 or 4 small incisions into the meat and insert the sliced garlic. place the shanks into a bowl and pour over the marinade, season and leave for about an hour or at least until your barbecue coals are ready.

Place directly over the coals to brown the meat, this should only take a few minutes each side.

Wrap the lamb shanks in a double layer of foil add the fresh mint. BBQ using the indirect method for 1 hour or longer if the BBQ is not too hot. To achieve even better results leave on the barbecue well away from the coals for 2 to 3 hours.

You will have to check the shanks each hour to add a little marinade (if required) to keep the meat moist.

To check if ready to eat, insert a fork into the meat if it's cooked through, only clear juices will run.
To make them extra special brush with redcurrant jelly (from a jar) a few minutes before the end of cooking.

Marinade
Add the rosemary and crushed garlic to the olive oil and season. Chop and add the fresh mint leaves or save for later to add to the foil wrap.

Note
If you don't add the mint to the shanks, you could add to some par boiled new potatoes and wrap with foil and place on the BBQ (indirect) for 20 minutes.